Refining triglyceride oils



United State Patfiflf O REFINING TRIGLYCERIDE OILS George C. Cavanagh,Fresno, Calitl, assignor to Ranchers Cotton Gil, Fresno, Calif.

No Drawing. Application January 3, 1955 Serial No. 479,653

8 Claims. (Cl. 260-424) The present invention relates to fluid refiningprocesses and more particularly to an improved water washing process foroils and other fluids immiscible with water.

The processing which crude oils of organic origin must receive inpreparation for market is largely dependent upon the purposes for whichthe refined oil is intended and the character of the crude oil. Mostanimal, fish and vegetable oils require refining, especially when theyare to be utilized as edible oils. For purposes of descriptivesimplicity, preliminary reference is made to the refining of cottonseedoil and the application of the subject invention thereto, although itwill later be understood that the invention is applicable to a widerange of oils and water immiscible fluids generally from which it isdesired to remove soap, fatty acids, alkali metals and other impuritieswhich are soluble in water, can be rendered soluble in water by thepractice of the invention or can be precipitated from both the oil andthe water by such practice.

Commercial refining of cottonseed oil frequently involves the treatmentof the crude oil with caustic soda. The removal of free fatty acids ofthe crude oil is effected by their combination with caustic soda to formsoap. This active ingredient may also be employedto extract coloringmatter by selective solvent action and to coagulate, destroy or rendernon-objectionable other minor impurities such as the lipides andgossypols. These impurities generally are rendered insoluble in oil bythe action of the caustic soda and with the soap are removed bysettling, centrifugation, selective solvent action, or the like.

Known refining processes for cottonseed oil and similar materials may bebriefly alluded to as the open kettle method which is now largelyobsolete but which Was popular prior to 1930; the continuous method ofcaustic soda refining involving the vigorous mixing of caustic soda andoil and the subsequent rapid heating followed by separation of theimpurities from the'refined oil by centrifugation; the modifiedcontinuous method in which soda ash solution is utilized to neutralizethe free fatty acids, coagulate phosphatides and minor impurities afterwhich the coagulated materials are removed by centrifugation; andrefining in miscella comprising the subject matter of my copendingUnited States patent application, Serial No. 366,458, entitledExtraction and Refining of Glyceride Oils and Fats From Source MaterialsThereof.

. All such refining methods have as a prime objective, as does thepresent invention, the rendering of a maximum yield of refined oil whichcontains a minimum of free fatty acids, color bodies, non-fattymaterials and other impurities.

It has previously been known in the various refining processes toWater-wash the refined oil as a final purifying step. This has been forthe purpose of removing water soluble impurities, principally alkalimetal soaps formed by the interaction of the alkali ions of causticsoda, soda ash, or the like with free fatty acids of the "ice oil. Formore highly refined oils, it has become the practice to repeat the waterwashing process. In such instances, refined oil is washed withapproximately 10% of water at about 180 F. in a first water-washcentrifuge maintained at a temperature of approximately F. In this firstwater-wash centrifuge, the oil is vigorously mixed with the hot water sothat as much as possible of the water soluble impurities are dissolvedin the water and the water and impurities held therein in solution aresubsequently separated from the oil by centrifugation. The procedure isthen repeated at approximately the same temperature in a secondwater-Wash centrifuge in which approximately 5% of hot water isutilized. The resultant oil usually contains approximately from 15 to 50parts per million of soap which is an adequate reduction for somepurposes but entirely inadequate for others.

Unfortunately, the vigorous agitation of the oils in the water-washcentrifuges frequently results in increased saponification and greaterrefining loss even though the resultant excessive soap may subsequentlybe removed.

To attain a lower soap content, it is the normal practice to pass thewater-washed oil, after drying, through filter cloths impregnated withactivated clays. This procedure is time consuming and expensive.Substantial portions of the oil are entrapped in the filter cloths andclays. Additional labor is required to control the filtering operationand the filter cloths and clays must be frequently cleaned, reactivated,and reinstalled for use. Unfortunately, odor and flavor reversionfrequently occurs during the filtration. At best, the filtration canonly be intermittently performed because of the down require-. ments forcleaning. In spite of these disadvantages, such additional purificationis commercially practiced because it has heretofore been the onlyfeasible method of reducing the soap content of the oil to levelsrequired for certain uses. Although the efiicacy of this final filteringthrough activated clays is dependent upon many variables, it hasfrequently proved capable of reducing the soap content of the ultimateoil to as low as two parts per million. For this reason, it hasheretofore been regarded as essential to perform the describedfiltration prior to hydrogenization. It should be noted thathydrogenization requires rior elimination of as much of the alkali metalions as possible, particularly .sodium ions. During hydrogenization,various nickel compounds are employed as catalysts. If alkali metals arepresent, they interact with the nickel compounds to produce toxicproducts undesirable in edible oils. Further, the efficiency of thecatalysts is impaired or destroyed by the presence of soap and/or alkalimetal ions.

It thus will be seen that the currently accepted fluid cleansingpractices of the character described are subject to major difficulties.The water washing steps, particularly if performed in two stages,require considerable volumes of water and are subject to waste waterdisposal problems. The best results attainable by current water washingprocedures do not sufficiently effectively remove soap from the oils formany purposes. The additional filtration to attain desired purity isexpensive, time consuming and frequently results in deterioration in thequality of the oil. Both the water washing and the fil tration areresponsible for excessive losses in oil although such losses haveheretofore been tolerated in order to gain adequate cleaning.

An object of the present invention is to provide an improved waterwashing process of the character described Which is far more eifectivein its cleansing action than previously attainable.

Another object is to make possible a more complete removal of soaps,alkaline reagents and other water soluble materials from refined oilsand the like.

Another object is to increase the efliciency ofthe water washingofrefined oils to applicable in this manner.- a a V t i The broad essencefoftthe present invention resides in the discovery that by adjusting theacidity of the water.

' V The hydrogen viously available by two stagewashingfollowed byfiltraj-tion through activated clays.

, Additional objects, are ito provide] a process of the characterdescribed which is economical'to perform, re-

quiresonly readily available apparatus, more rapidly attains effectivesoap removal than previously possible,'incurs less loss-in oil thanconventionally incurred, and

V is fully. efiective in performing its intended functions with-toutfodor or flavor reversion. T

such an extent that a single stage washing operation can attain the bestresultsprev Further objects and advan'tages 'will become'apparent "inthe'subsequentdescription. t

=Aspre'viously alluded to, conventionalwater-wash cen- V 'trifugesreceive therefined oiltto bewashed, vigorously intermixand agitatewatertherewith to dissolve the water 7 soluble. constituents thereof; andsubsequently separate the oil and water in the well known'centrifugalmanner by takingadvantage of the difierences in their specific: t'gravities. 'It has been known to water' wash other than pure oil,'suchas miscellasof'oilsin' solvents therefor, and

other materials which are immiscible with oil, and it is 7 Moreprecisely defined, during the water Washingop'eration the hydrogen ion.concentration should substantially equal the alkali metalion'concentration'. amount of ner described where greater purification,was required.

In employing the present invention, no filteringtis required.

Currently, by the practice of the presentinvention I' iwith the sameequipment, the same type of oil andhexane: 1

miscella' is flowed through the water-wash centrifuge at f a rate ofgallons of miscella perminute' One to five to be understood that thepresent invention is also broadly so thatt there is about'l gramequivalent of hydrogen ions tor'each 1 gram equivalentofthe aggregatealkaline metals" contained .thefoil and water mixture during "agitation,a vastlyv improvedfzcleansing action, soap removal, and minimizing ofadditional soap formation is attained; V V

ions replace the alkali metal ions of the soap during'agitation'to.convert the same. to the related fatty acids. The-fattyacidsfare'dissolved in oil but, are

present in such minute amounts that the oil is notdeleteriously'efiected; Subsequent deodorization at temperatures above350 E andvacuumi .of 5 to 15 mm. of mer cury remove the last'traces offatty acids. The' released alkaliimetalgions combine with'the negativeions of the acidemploy'ed to form salts which are insoluble in oil.

Wherethe soap involved is a calcium soap, it' is also insoluble in waterbut, readily precipitates andthusiseasily removed. 5 In on refiningprocesses the soap is rarely that i of calcium but: most frequently ofsodium or occasionally potassium. The sodium and potassium salts arewater soluble and thus readily removed in aqueous solution.

' Similarlyanyfree ions of; thejalkali rnetals are rendered readilyremovable by interaction withthe negative ions of the acid employed andare thus. not available for acl-' ditional-soap formation. i

The water used for oil washing purposes is acidulated by the additionthereto of any suitable acid-of mineralor organic origin. because theyare cheaper and relatively stronger. Citric acid, however, has beenparticularlyuseful in this respect,

because of its sequesteringaction on metal ions; Inasmuch asiit is thepractice in continuous refining processes,

to direct a continuous stream of Water through the waterwashcentrifuges, theacid is conveniently imparted tothe water 'by aregulated flow thereof into the stream ,prior to its passage'into thewater-wash centrifuge. Manyjsuittion- Offlfl'lfi water must beat,-,least about .01 normal and the resultant acidic aqueous bath'isfound to have a pH of approximatel-y 'l, There'is no'criticalpreciseupper V limit to the amount of acid that may be employed but hydrogenion concentrations in excess of .033' merely con-j stitute waste wherethe soap 'content is less than about I iO pat s per: million; and, tesors. ha 5 parts. per million ct -he acida e emnley d,. i caus s-a ka ss ndi color i lit-r sen o; dis olv ac n o the 93* a t ou h Mineral acidsare normally preferred 7 gallonspof watertper minute are flowedthroughthe water- Washcentn'fuge for the-washingtpurpo'seg' Thus,thewwater: makes up',.;from 5%"to20.% by volume, of themiscella i andwatermixtureain. the centrifuge; This proportion is similar to thatconventionally employed. From to 100, Y 7 drops sulfurioacidoffifi? Baum(98%) concentration, Y are; d livered t0 the'water 7 prior to its:introductio'ntto "the centrifuge. Sulfuric acid is economicalto"employfis insoluble in both, the oil and, hexane and thus/excellentlysuited to theqpurposeti ,Anybtheracid'insoluble in oil Q and hexanecould be" employedflin' equivalent; amounts; Reference has beenpreviously made touthe desirable at sequestering action. of citric acid.Oxalic'acid is alsoa 1 a Y good sequestering agent but should not beusedin earner" The resultantacidulated water bath has a hydrogen" ionconcentration of from .01 tov .033normal' and" is excellently suited tothe purposeJAs. the bath'isvigor usIy mixed with the oil in thecentrifuge,the conventional llh' re se. in: saponification incident tothe vigorous agitation no longenoccurs; The hydrogenionsconvertlthe soapT P iQU Y formed, into. their. related fatty acids. T Theis'ulfate, ionsof the acid interact with the'sodium ions released from the} soap toformsodiumsulfate: whicliiisreadily dissolved: in the water.v Anyfree-alkali metalions eon- V tained by the oil are similarly combinedwith. negative ions of the acid to form aisalt. In the'usualmannentha twater-washgcentrifuge then separates'the w'aterlwith the alkali metalsaltsand other impurities therein fromfthe' miscella, In normalpractice, soap is present'at-this;stage in the oil in at least about 15to 50 parts'-per-million.- f Under the described practiceof;:the-presentinvention,"

however,thesoaprcontent isjreducedqto approximately 2 7 parts permillionjhusobviating thev necessitylof asecond 7 I twillbe-apparentthatthe invention can be-performedasabatch'QpdlfltlQIlffilthQllgh: described in its-continuous, Iembodiment-betterj'suitedto currentgcomrnercialpractices; It not onlyattains; superior cleansingresuks but requires;less;equipment,ilessivlahorrand avoids the eirpenses'anddifficulties'incident toffiltrafion; The more'thorough re moval 1 ofthe; alkali-metal; 'ions' minimizes. formation of toxic niclgel:products, during [subsequent hydrogeniz'a j tion. Lesswa-ter is requiredfor washing purposesand maller disposal problem for. the. water results;2 Refininglosses: incident to increased.saponification injthe water-:-fwash centrifuges and 'incident'to entrapment inffilte'r s'is' E Vavoidedit Thele rpe'nse of thefacid is obviously negligible; :While theinveriti'on has been illustrated and described f infwhat'is at presentr'egarded as 'theinost practical and preferred embodiment, it isrecognized that departures. a ba lad her m w h r m scope, oft ei ie h Iwhi ch is. not tobe. limited to the details disclosed'herein but tojb aqr edt e t llsmm of he so an. 1 1 enthtace anyandall equivalentrnethodsandprocesses, 1 1

. Hayingidesbfihedmy.'inveution,- what I .claimiasnjnew; 1

an sw mm rs! lark t stia eat s ass ses l. A continuous process forremoving soapstock from a miscella of alkali refined cottonseed oil in asuitable solvent therefor comprising flowing the miscella in a streamthrough a water washing apparatus, flowing water in a stream throughsaid washing apparatus wherein the water is intimately mixed with themiscella and subsequently separated therefrom, and adding acid to thewater stream in advance of the washing apparatus in a quantitysutficient to attain a normal hydrogen ion concentration of from atleast about .01 to .033 in the Water stream, said stream as it entersthe water washing apparatus consisting substantially entirely of theacid and water.

2. A process for water washing a miscella of alkali refined cottonseedoil in hexane containing traces of alkali metal soap comprising formingan acidulated aqueous solution of .01 to .033 normal of an acid which issubstantially insoluble in cottonseed oil and in hexane, the aqueoussolution consisting substantially entirely of water in addition to theacid employed, and intimately mixing the aqueous solution inapproximately to 20% by volume With the miscella.

3. A process for water washing a miscella of alkali refined cottonseedoil in hexane containing traces of alkali metal soap comprising formingan aqueous solution of sulfuric acid of a strength of .01 to .033 normalwith the remainder of the solution consisting substantially entirely ofwater, intimately mixing the acid solution with the miscella whereby thehydrogen ions of the aqueous solution replace the alkali metal ions ofthe soap to form water soluble salts, dissolving said salts in theaqueous solution, and separating the aqueous solution with the saltsdissolved therein from the miscella.

4. A process of further refining an alkali refined triglyceride oil inmiscella containing traces of soapstock comprising converting theresidual traces of soapstock in the miscella to free fatty acids andwater soluble salts by intimately mixing an aqueous acid solution,containing an acid in a quantity suflicient to provide an hydrogen ionconcentration of from about .01 to .033 normal with substantially all ofthe remainder of the solution being water, with the miscella whereby thefree fatty acids dissolve in the miscella and the salts dissolve in thewater of the aqueous solution; removing the aqueous solution containingthe water soluble salts from the miscella containing the free fattyacids; and subsequently extracting the free fatty acids from themiscella.

5. A process for further refining an alkali refined triglyceride oil ina miscella of a suitable solvent for the oil, which miscella containstraces of soapstock formed by the interaction of alkali with free fattyacids of the oil comprising washing the miscella with an aqueoussolution of an acid which is substantially insoluble in the miscella toreconvert the traces of soapstock into free fatty acids which dissolvein the miscella and into water soluble salts which dissolve in the waterof the aqueous solution, the aqueous solution containing the acid in aquantity sufficient to provide an hydrogen ion concentration of fromabout .01 to .033 normal with substantially all of the remainder of thesolution being water, removing the aqueous solution and dissolved saltsfrom the miscella, and subsequently subjecting the miscella to a vacuumto extract the solvent and fatty acids from the oil.

6. In the alkali miscella refining of triglyceride oil in a suitablesolvent therefor in which free fatty acids of the oil are converted intosoapstock and the soapstock is subsequently extracted from the miscellato an extent leaving from approximately 15 to 50 parts per million ofsoapstock dissolved in the miscella and making available alkali metalions of the soapstock, the steps of reacting an acid which issubstantially insoluble in the oil and in the solvent with the soapstockwhile in aqueous solution to form free fatty acids which dissolve in themiscella and water soluble salts which dissolve in the water, saidaqueous solution consisting of acid in a quantity suflicient to providean hydrogen ion concentration substantially equal to the alkali metalion concentration of the soapstock in the miscella and the remainder ofthe solution being substantially entirely water, removing the watercontaining the soluble salts from the miscella containing free fattyacids, and subsequently extracting the free fatty acids from themiscella at a temperature of approximately 350 F. and under a vacuum offrom substantially 5 to 15 millimeters of mercury.

7. A process for water Washing a miscella of alkali refined cottonseedoil in hexane containing traces of sodium soap of the fatty acids of theoil but from which substantial portions of said soap and color bodieshave already been removed comprising intimately mixing an aqueoussolution of sulphuric acid of a strength of approximately .01 to .033normal with the miscella whereby hydrogen ions of the acid solutionreplace the sodium ions of the soap to form a resultant water solublesalt which dissolves in the aqueous solution and whereby the soap isconverted into fatty acid which dissolves in the miscella, said aqueoussolution in addition to the sulphuric acid being substantially entirelywater, and subsequently extracting the fatty acids from the miscella.

8. In a process of further refining an alkali refined triglyceride oilin miscella containing approximately 15 to 50 parts per million ofsoapstock in the miscella, the steps of flowing the miscella andsoapstock through a water wash centrifuge, and flowing an aqueous acidsolution through the centrifuge with the miscella in a quantity of fromabout to /5 of the quantity of the miscella, the

aqueous solution consisting substantially entirely of water i and anacid in a quantity sufiicient to provide from about .01 to .033 normalhydrogen ion concentration in the solution whereby the soapstock in themiscella is reconverted to free fatty acids which dissolve in themiscella and into water soluble salts which dissolve in the aqueoussolution.

References Cited in the tile of this patent UNITED STATES PATENTS1,147,392 Hagemann July 20, 1915 2,374,924 Clayton May 1, 1945 2,510,379Christenson June 6, 1950 2,654,766 Taussky Oct. 6, 1953 2,739,164 WeberMar. 20, 1956 FOREIGN PATENTS 886,365 France Oct. 13, 1943

4. A PROCESS OF FURTHER REFINING AN ALKALI REFINED TRIGLYCERIDE OIL INMISCELLA CONTAINING TRACES OF SOAPSTOCK COMPRISING CONVERTING THERESIDUAL TRACES OF SOAPSTOCK IN THE MISCELLA TO FREE FATTY ACIDS ANDWATER SOLUBLE SALTS BY INTIMATELY MIXING AN AQUEOUS ACID SOLUTION,CONTAINING AN ACID IN A QUANTITY SUFFICIENT TO PROVIDE AN HYDROGEN IONCONCENTRATION OF FROM ABOUT .01 TO .033 NORMAL WITH SUBSTANTIALLY ALL OFTHE REMINDER OF THE SOLUTION BEING WATER, WITH THE MISCELLA WHEREBY THEFREE FATTY ACIDS DISSOLVE IN THE MISCELLA AND THE SALTS DISSOLVE IN THEWATER OF THE AQUEOUS SOLUTION, REMOVING THE AQUEOUS SOLUTION CONTAININGTHE WATER SOLUBLE SALTS FROM THE MISCELLA CONTAINING THE FREE FATTYACIDS, AND SUBSEQUENTLY EXTRACTING THE FREE FATTY ACIDS FROM THEMISCELLA.